Simulated digital radar system with earth curvature and atmospheric effects

Abstract

A training cockpit on a hydraulic motion system is responsive to the cockpit controls to simulate an aircraft in flight. A simulated radar display of the aircraft vicinity is provided from a data base memory of the topographic and cultural data of the gaming area. As the antenna scans, particular blocks of data are transferred from the district memory to smaller sector core memories at high speed access and transfer rates. The sector memory provides a line of data for each sweep of the simulated radar. Reflectance and elevational data is retrieved from the sector memories and processed, one sweep at a time, through digital radar equation computation equipment which calculates the brightness of each spot in the simulated radar display. This digital brightness data is processed through an earth curvature subsystem which modifies the brightness in accordance with the horizon effect. The modified brightness is applied to a digital to analog converter and then to the radar display. A central computer coordinates the data flow with the flight parameters-position, speed, altitude, direction, etc., of the simulated aircraft.

I claim: 
     
       1. An earth curvature correction circuit adapted for use in a digital radar landmass system for accumulatively decreasing the terrain elevation of each range point thereof to simulate the effect of the earth's curvature, comprising: a range point counter having an output which increases during each sweep line and which remains proportional to the current range point;   a curvature control having an output proportional to the desired radius curvature;   a multiplier which forms the product of the range output of the counter and the curvature output of the control;   an adder which forms the sum for each range point of the multipler product plus the multiplier product for the previous range point; and   output register for temporarily holding the sum for each range point for outputting and for returning each sum to the adder to be added to the next range point product to form the next range point sum.   
     
     
       2. The circuit of claim 1, wherein: the output of the range point counter is n and increases for each range point;   the output of the curvature control is a constant K;   the output of the multiplier is Kxn;   the output of the adder is Kxn + EC n-1  where EC n-1  is the earth curvature correction output of the previous range point n-1; and   the output of the output register is EC n  = K(n 2  + n).   
     
     
       3. The circuit of claim 2, wherein the curvature control constant K represents the curvature of the earth and atmospheric effects. 
     
     
       4. The circuit of claim 2, wherein the curvature control constant K represents only the curvature of the earth. 
     
     
       5. The circuit of claim 2, wherein K may be increased or decreased.